Safe handling of hazardous substances – requirements for tank systems for liquid raw materials such as electrolytes and NMP

Large quantities of hazardous liquids are required in the manufacturing process of lithium-ion batteries. Special requirements are therefore placed on storage and distribution, both in terms of the regulatory framework and process handling. Safety technology plays an important role.

The manufacture of battery storage systems, from the cell to the finished module, involves numerous production steps. Liquid media play a role in the following process steps in particular:

• Mixing the active material (electrode production)
• Drying the electrodes (electrode production)
• Electrolyte filling (cell assembly)
• Potting (pack production).

During the production of the coating materials for the electrodes, solvents are added to the active materials in special mixing and dispersing systems. As a rule, NMP (1-methyl-2-pyrrolidone battery grade) is used for this purpose. This is a reprotoxic, harmful and irritating liquid. Due to its hazardous properties, its use has been restricted by the European Commission and a substitution requirement has been imposed. So far, however, no suitable alternatives have become established on the market. Special measures and best practices for limiting and monitoring hazards during use must therefore be taken into account. The ECHA (European Chemicals Agency) guidelines on compliance with restriction 71 of the REACH Regulation go into this in more detail.

This NMP is recovered as solvent vapor during the drying process of the electrodes and is recovered in special condensation and distillation plants at a rate of over 95% and made available for the mixing process again. Waste water and liquid residues must be stored properly and made available for disposal or reuse. At the end of the assembly step, the cells are filled with electrolytes to ensure charge exchange in the battery. The electrolytes are usually customer-specific formulations in which conductive salts are dissolved in solvents such as EMC (ethyl methyl carbonate) or DMC (dimethyl carbonate). Electrolytes are also water-polluting and flammable liquids. To ensure storage stability, the electrolytes must be used in certain temperature ranges and be superimposed with inert gas. The solvents themselves must be provided in pure form via rinsing processes and the rinsing quantities must be collected in suitable containers.

Packing the cells

In pack production, the housings with the cells are partially or completely filled or embedded with a compound to make them shock and vibration resistant and to create a seal against moisture, solvents and corrosive substances. This process is called “potting”. Potting compounds are also used for electrical insulation, flame retardancy and heat dissipation. The most common types of potting compounds are polyurethane, acrylic, epoxy resin and silicone. However, each of these chemical compounds has its own physical and hazardous properties. Special measures must be taken when handling and storing polyurethane. Göhler Anlagentechnik from Hösbach/Northern Bavaria has been involved in the planning, construction, maintenance and servicing of process engineering systems, especially tank systems for hazardous media, for over 70 years. With over 300 employees at several locations in Germany. Göhler also has excellent references in the relatively young market of large-scale battery production. Thanks to its market knowledge in the automotive sector as well as in the chemical trade and chemical industry, automotive groups that now want to manufacture batteries can benefit from the plant manufacturer’s experience in both sectors.

Warehouse planning

To ensure that the media required for uninterrupted production operations can be made available, the operator must have sufficient stocks. There are numerous requirements and framework conditions for storage. The legal framework is essentially provided by TRGS 509 (Storage of liquid and solid hazardous substances in stationary containers and filling and emptying points for portable containers) and TRGS 510 (Storage of hazardous substances in portable containers). Other regulations must also be complied with.

Some examples of this are

• BImSchVO,
• WHG with AwSV,
• Pressure Equipment Directive,
• Atex regulations

Detailed planning is necessary in order to take into account this multitude of regulations as well as product and customer requirements. The implementation of order-specific requirements plays an important role here, which requires a thorough needs analysis. The benefit for the client is the top priority. In addition to the storage volumes, the dispensing capacities and the pressure and temperature specifications, the interfaces of the tank systems must also be clarified:

• What are the environmental conditions (e.g. indoor/outdoor installation, as well as earthquakes)?
• Which containers are used to deliver the media (coupling types, discharge pump or nitrogen discharge, quantities, quantity recording, etc.)?
• Which product requirements (e.g. temperature control, inertization, residual oxygen/residual moisture) apply?
• Is the data available at the transfer points (volume flow, pressure, temperature)?
• Which interfaces to external systems (e.g. e-fill machines, mixing, NMP recovery, distillation system, foaming machine) are required?
• Which electrical interfaces and data connections are required? Is traceability required?
• How are the supply and disposal systems (exhaust air/heating/cooling, nitrogen, compressed air, drainage) installed?
• How high are CAPEX/ OPEX?

The Göhler experts work out the required parameters. With these specifications, the system can be planned and designed in detail. In addition to the specification for tanks and pumps, the design of the safety fittings such as flame arresters is also crucial for a safe tank system. The classification of PL/ SIL categories, which result from a risk analysis and a joint HAZOP with the user, are fundamental for further implementation planning. The design of the sensors and monitoring systems such as oxygen meters and gas warning systems round off the topic – and all of this is in the required ATEX category. The system operator must also address other issues such as fire and lightning protection. Finally, a defect-free acceptance by the Z.S (authorized inspection body) is expected. The inerting system also requires careful design in order to comply with the required product quality or the inerting level in accordance with TRGS. This also includes calculating the initial inertization as a dilution flush to ensure the maximum permissible residual oxygen content. The storage media are often water-polluting substances. A WHG-compliant loading and unloading area with a suitable average system and the associated calculation in accordance with TRWS 779 is therefore unavoidable. Depending on the type of container (single or double-walled), drip pans with a suitable solid construction are required.

Mechanical and electrical realization of the system

Once the planning has been completed, the next project phase is initiated: the mechanical and electrical implementation of the system. With a large proportion of pre-assembly at the manufacturer’s plant, the workload on the construction site can be reduced. All the trades required for plant construction must work together smoothly and hand in hand: from tank installation to steel and pipeline construction, temperature control and insulation through to electrical cabling. High safety requirements for the execution of the work are a matter of course today. Employee health and environmental protection are essential. Careful processing of the materials is also a mandatory requirement. Finally, there must be no metallic particles in the medium to prevent a short circuit within the battery cell. This is why special filters are also included in the process engineering design. Commissioning with repeated flushing of the system and sampling is therefore of great importance and essential for the client and user. The quality demands on the specialists and the system are high! Prior to acceptance, the user and the acceptance authorities are provided with the necessary documentation. These often contain several meters of paper folders. Among these, one document is particularly important: the CE certificate of conformity in accordance with the Machinery Directive and the applicable regulations. The system may not be put into operation without this certificate! A number of cell factories are currently being planned in Germany and Europe, and speed to market for the finished battery is an extremely important factor. The implementation of a tank storage project requires the early involvement of planners and plant engineers with sufficient capacity and specialist personnel.

Maintenance and service

However, the specialist company does not stop after acceptance and handover. The new tank system must be regularly maintained in accordance with WHG, TRGS and the Ordinance on Industrial Safety and Health and the manufacturer’s specifications, especially the safety-related components. Careful maintenance and servicing is the only way to ensure a long service life and trouble-free operation of the system.

Good and early advice and planning

The manufacture of tank systems to supply battery production places high demands on planning, construction and maintenance. The operator of the systems is therefore well advised to contact specialist companies with the relevant expertise at an early stage. Due to the hazardous media, many regulations must be taken into account during implementation. Only many years of experience and a high level of knowledge can guarantee a high level of safety and quality and offer the producer legally compliant planning, implementation and safe operation.

Author:

Martin Zang,

Technical Manager